US11229459B2 - Polyaxial bone screw with increased angulation - Google Patents

Abstract

A polyaxial bone device includes a screw, a screw housing, and a spring. The screw includes a screw head and a shaft that extends from the screw head. The screw housing defines a longitudinal axis and a bore that extends along the longitudinal axis. The screw housing includes a basewall and opposed sidewalls that extend from the basewall. The basewall defines a notch that receives the shaft to increase pivotal movement between the screw and the screw housing relative to the longitudinal axis of the screw housing. The opposed sidewalls define a rod-receiving channel. The screw housing defines a transverse hole in communication with the bore. The spring is supported in the transverse hole and extends therethrough. The spring extends into the bore to frictionally engage the screw head while the screw head is seated in the bore.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 15/664,398, filed on Jul. 31, 2017, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to spinal surgery, and more particularly to polyaxial bone screws with increased angulation.

BACKGROUND OF THE INVENTION

The spinal column is a complex system of bones and connective tissues that provide support for the human body and protection for the spinal cord and nerves. The adult spine is comprised of an upper and lower portion. The upper portion contains 24 discrete bones, which are subdivided into three areas including 7 cervical vertebrae, 12 thoracic vertebrae and 5 lumbar vertebrae. The lower portion is comprised of the sacral and coccygeal bones. The cylindrical shaped bones, called vertebrae or vertebral bodies, progressively increase in size from the upper portion downwards to the lower portion.

An intervertebral disc along with two posterior facet joints cushion and dampen the various translational and rotational forces exerted upon the spinal column. The intervertebral disc is a spacer located between two vertebral bodies. The facets provide stability to the posterior portion of adjacent vertebrae. The spinal cord is housed in the canal of the vertebral bodies. It is protected posteriorly by the lamina. The lamina is a curved surface with three main protrusions. Two transverse processes extend laterally from the lamina, while the spinous process extends caudally and posteriorly. The pedicle connects the lamina to the vertebral body.

The spine is a flexible structure capable of a large range of motion. There are various disorders, diseases, and types of injury which restrict the range of motion of the spine or interfere with important elements of the nervous system. The problems include, but are not limited to scoliosis, kyphosis, excessive lordosis, spondylolisthesis, slipped or ruptured discs, degenerative disc disease, vertebral body fracture, and tumors. Persons suffering from any of the above conditions may experience extreme or debilitating pain and diminished nerve function. These conditions and their treatments can be further complicated if the patient is suffering from osteoporosis, or bone tissue thinning and loss of bone density. Spinal fixation apparatuses are widely employed in surgical procedures for correcting spinal injuries and diseases. When the disc has degenerated to the point of requiring removal, there are a variety of interbody implants that are utilized to take the place of the disc. These include polyetheretherketone (“PEEK”) interbody spacers, metal cages, and cadaver and human bone implants. In order to facilitate stabilizing the spine and keeping the interbody in position, other implants are commonly employed, including longitudinally linked rods secured to coupling elements, which in turn are secured to the bone by spinal bone fixation fasteners such as pedicle screws utilized to facilitate stabilization of bone.

BRIEF SUMMARY OF THE INVENTION

In general, the present disclosure is directed to a polyaxial bone screw device including a screw and a screw housing. The screw housing defines a longitudinal axis and a notch configured to receive a portion of the screw. The notch is configured to enable increased angulation of the screw relative to the longitudinal axis of the screw housing in response to relative pivotal movement between the screw and screw housing. The polyaxial bone screw device may include a spring that is positioned to frictionally engage the screw to maintain the screw in an angled position relative to the screw housing.

In accordance with an aspect of the present disclosure, a polyaxial bone screw device includes a screw, a screw housing, and a spring. The screw includes a screw head and a shaft that extends from the screw head. The screw housing defines a longitudinal axis and a bore that extends along the longitudinal axis. The screw housing includes a basewall and opposed sidewalls that extend from the basewall. The basewall defines a notch configured to receive a portion of the shaft therein. The notch is configured to selectively increase pivotal movement between the screw and the screw housing relative to the longitudinal axis of the screw housing in the direction of the notch. The opposed sidewalls define a rod-receiving channel. The screw housing further defines a transverse hole that is in communication with the bore. The spring is supported in the transverse hole of the screw housing and extends therethrough. The spring extends into the bore of the screw housing to frictionally engage the screw head of the screw while the screw head is seated in the bore of the screw housing.

In disclosed embodiments, the spring may be configured to maintain the shaft at an angular position relative to the longitudinal axis of the screw housing while frictionally engaged with the screw head.

In certain embodiments, the screw head may include an outer surface that is configured to facilitate frictional engagement with the spring.

In some embodiments, the polyaxial bone screw device may further include an anvil disposed within the screw housing and positioned to support a spinal rod seated within the rod-receiving channel. The anvil may be seated on the screw head while a portion of the anvil is configured to engage the spring. The spring may be frictionally engaged with the screw head while engaged to the portion of the anvil to support the screw in a position relative to the screw housing.

In disclosed embodiments, the screw housing may be pivotable in a first direction relative to the screw to a first angle and may be pivotable in a second direction relative to the screw to a second angle. The first angle may be different than the second angle. The shaft of the screw may be positioned within the notch of the screw housing while disposed in the first angle.

In certain embodiments, the first angle is about 60 degrees relative to the longitudinal axis of the screw housing and the second angle is about 45 degrees relative to the longitudinal axis of the screw housing.

In disclosed embodiments, the polyaxial bone screw device may further include a pin disposed within the transverse hole to support the spring therein.

In some embodiments, the polyaxial bone screw device may further include a set screw configured to be threadably received within the screw housing to secure a spinal rod within the screw housing.

According to another aspect of the present disclosure, a method of securing a spinal rod to a polyaxial bone screw is provided. The method includes inserting a polyaxial bone screw into bone. The polyaxial bone screw has a screw, a screw housing, and a spring. The screw has a head and a shaft extending therefrom. The shaft is insertable into bone. The screw housing includes opposed sidewalls that define a U-shaped rod-receiving channel. The screw housing further defines an opening for receiving the head of the screw, a notch for receiving a portion of the shaft, and a transverse hole. The spring extends through the transverse hole and is maintained by a pin disposed within the transverse hole.

The method includes positioning the screw housing relative to the screw. The screw housing is movable in a first direction relative to the screw to a first angle. The screw housing is movable in a second direction relative to the screw to a second angle. The first angle is greater than the second angle when the portion of the shaft of the screw is received in the notch of the screw housing at the first angle when the screw housing is moved in the first direction. The method further includes supporting the portion of the shaft in one or both of the first and second angles through frictional engagement between the spring and the head of the screw. The method includes coupling a spinal rod to the polyaxial bone screw by inserting a portion of the spinal rod into the U-shaped rod-receiving channel of the screw housing of the polyaxial bone screw.

The method may further include selectively pivoting the screw along a longitudinal axis of the spinal rod in the first direction relative to the screw housing to the first angle. Positioning the screw housing may include positioning the portion of the shaft within the notch such that the first angle is about 60 degrees relative to the longitudinal axis of the screw housing.

The method may further include selectively pivoting the screw along a longitudinal axis of the spinal rod in the second direction relative to the screw housing to the second angle. Positioning the screw housing may include positioning the portion of the shaft within another region of the screw housing that is separate from the notch such that the second angle is about 45 degrees relative to the longitudinal axis of the screw housing.

The method may include securing the spinal rod to the polyaxial bone screw by attaching a set screw to the screw housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the disclosure and, together with a general description of the disclosure given above, and the detailed description of the embodiments given below, serve to explain the principles of the disclosure, wherein:

FIG. 1 is an exploded view, with parts separated, of a polyaxial bone screw in accordance with the present disclosure;

FIG. 2A is a perspective view of the polyaxial bone screw ofFIG. 1 with a set screw thereof removed for clarity;

FIG. 2B is a side, perspective view of the set screw of the polyaxial bone screw ofFIG. 1;

FIG. 3 is a side view of the polyaxial bone screw ofFIG. 2A;

FIG. 3A is a side view of a screw housing of the polyaxial bone screw ofFIG. 1;

FIG. 3B is a bottom perspective view of the polyaxial bone screw ofFIG. 3;

FIG. 4 is a cross-sectional view of the polyaxial bone screw ofFIG. 3 taken along section line4-4;

FIG. 4A is a cross-sectional view of the screw housing ofFIG. 3A taken alongsection line4A-4A;

FIG. 5 is a front view of the polyaxial bone screw ofFIG. 2A;

FIG. 5A is a bottom view of the polyaxial bone screw ofFIG. 5;

FIG. 6A is a side view of the polyaxial bone screw ofFIG. 2A shown coupled to a spinal rod with the screw shaft depicted at a first angle relative to the screw housing;

FIG. 6B is a side view of the polyaxial bone screw ofFIG. 2A with the polyaxial bone screw depicted at a second angle relative to the screw housing;

FIG. 7 is a perspective view of the polyaxial bone screw ofFIG. 2A inserted into bone; and

FIG. 8 is a perspective view of the polyaxial bone screw ofFIG. 6A.

DETAILED DESCRIPTION

Embodiments of the present disclosure are now described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. As commonly known, the term “clinician” refers to a doctor, a nurse, or any other care provider and may include support personnel. Throughout the description, the term “proximal” refers to a portion of structure (e.g., a device or component thereof) closer to the clinician, while the term “distal” refers to a portion of structure farther from the clinician. Additionally, in the drawings and in the description that follows, terms such as “top,” “bottom,” “front”, “back,” “side,” and similar directional terms are used simply for convenience of description and are not intended to limit the disclosure.

In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

With reference toFIGS. 1, 2A and 2B, apolyaxial bone screw10 generally includes ascrew housing20, ananvil30, a spring40 (e.g., a compression spring), apin50, ascrew60, and aset screw70. Thepolyaxial bone screw10 is configured to be cooperatively engaged to a spinal rod “R” (FIGS. 6A and 6B).

With reference toFIGS. 3-5A, thescrew housing20 of thepolyaxial bone screw10 defines a longitudinal axis “L” and has a generally cylindrical shape. Thescrew housing20 extends from aproximal end20adefining aproximal opening21ato adistal end20bdefining adistal opening21b. The proximal and distal ends20aand20b, respectively, of thescrew housing20 may be disposed in parallel relation. Thescrew housing20 further includes opposing first andsecond sidewalls20c,20dthat extend proximally from thedistal end20bof thebasewall20fof thescrew housing20 and define a generally U-shaped rod-receivingchannel22 therebetween. Each of the first andsecond sidewalls20c,20ddefines an externalflanged recess23 that is configured to facilitate grasping of thescrew housing20 by an instrument (not shown) that can also be used to facilitate insertion of thepolyaxial bone screw10 into a vertebral body.

Theannular basewall20fof thescrew housing20 extends distally to thedistal end20bof thescrew housing20. Thescrew housing20 defines a threadedinternal surface20eand a rod slot or rod-receivingchannel22 through a proximal portion of thescrew housing20, and acentral bore24 through thescrew housing20 from theproximal opening21adefined in theproximal end20aof thescrew housing20 to thedistal opening21bdefined in thedistal end20bof thescrew housing20. The rod-receivingchannel22 is configured to receive a spinal rod “R” (FIGS. 6A and 6B) therein and the threadedinternal surface20eis configured to threadably receive a set screw70 (FIG. 2B) for securing the spinal rod “R” in thescrew housing20. Theannular basewall20fof thescrew housing20 includes acentral portion20galigned with the rod-receivingchannel22 and first andsecond side portions20h,20ialigned with the first andsecond sidewalls20c,20d, respectively. Thefirst side portion20hof theannular basewall20fdefines atransverse hole26 that receives thespring40 andpin50. Thetransverse hole26 is in communication with thebore24 to enable thespring40 to extend through thebasewall20fand into thebore24. Thecentral portion20gof theannular basewall20fincludes afront wall20jand a back wall20k. Thescrew housing20 defines a relief groove or notch28 that may be milled out of theannular basewall20f. Although shown as positioned on thefront wall20j, thenotch28 may be positioned at any suitable location along thebasewall20f(e.g., back wall20k,first side portion20h, second side portion20i, etc.). In this regard, it will be appreciated that while the notch is shown disposed onfront wall20j, such that when the screw pivots in the direction of the notch it pivots parallel to a rod disposed in the rod slot, the notch may be disposed in one ofside walls20h,20isuch that when the screw pivots in the direction of the notch it pivots perpendicular to or at an angle with respect to the direction of the rod slot, or a rod disposed in the rod slot.

With reference to FIGS, thenotch28 is defined by aplanar surface28aconnected toarcuate surfaces28b(e.g., defined by a diameter ranging from about 0.092 inches to about 0.096 inches in certain embodiments) disposed on opposite ends of theplanar surface28a. Each of thearcuate surfaces28bextends distally from theplanar surface28ato anglededges28c. The angled edges28c, which in certain embodiments, may be angled about 45 degrees relative to the longitudinal axis “L,” extend to thedistal end20bof thescrew housing20. In certain embodiments, the diameter of thedistal end20bof thescrew housing20 may be about 0.275 inches. In certain embodiments, the height of thenotch28 relative todistal end20bmay range from about 0.034 inches to about 0.038 inches. Although thenotch28 is shown to extend along an arc angle of about 60 degrees (e.g., 30 degrees from centerline/midpoint thereof) around a circumference of thescrew housing20, thenotch28 may, in some embodiments, extend around a greater or lesser arc angle, e.g., up to about 180 degrees. In some embodiments, the arc angle may measure up to about 90 degrees. In embodiments, the arc angle may measure up to about 30 degrees. In general, dimensions of thenotch28 will depend upon the amount of angulation and/or dimensions ofscrew60.

The centerline/midpoint of thenotch28 may be aligned with an axis of the U-shaped rod-receiving channel22 (FIGS. 3A and 3B). In some embodiments, the centerline/midpoint of thenotch20 may be positioned such that thenotch28 is rotationally offset from the axis defined by the U-shaped rod-receivingchannel22.

As can be appreciated, one or more of the dimensions of thenotch28 disclosed herein may be provided to enable thepolyaxial bone screw10 to achieve an increased angulation of about 15 degrees (e.g., up to 60 degrees in a first pivot angle as compared to 45 degrees in a second pivot angle). The ratios of two or more of the disclosed dimensions may be predefined to enable such increased/optimized angulation (e.g., height ofnotch28 to degree of angulation).

Referring toFIGS. 4 and 4A, theannular basewall20fof thescrew housing20 further includes aninternal surface25 that defines aseat25afor supporting thehead62 of thescrew member60 at an internal location spaced-apart from, and proximal to, a distal end of thescrew housing20. Theseat25aextends to aninner edge25b, which may be C-shaped, and which includes first and second ends25c,25dthat circumferentially terminate at thenotch28. Theinner edge25bis disposed adjacent to theangled edges28cof thenotch28 and thedistal end20bof thescrew housing20. In some embodiments, theseat25ahas a diameter ranging between about 0.219 inches to about 0.223 inches.

Referring again toFIGS. 1 and 4, thescrew member60 of thepolyaxial bone screw10 includes a head62 (e.g., spherically-shaped) that is positioned in contact with theseat25aof thescrew housing20 to support thescrew member60 in thescrew housing20, aneck63 that extends distally from a distal end of thehead62 to a threadedshaft64. The threadedshaft64 extends distally from a distal end of theneck63 to a distal end of thescrew member60. Thehead62 includes a textured or uneven outer surface62a(e.g., annular ribs, ridges, etc.) that is configured to frictionally engage with thespring40 while thespring40 is engaged with theanvil30 to maintain thescrew member60 in position relative to thescrew housing20. Thehead62 defines a driving recess62b(e.g., hexolobular or the like) defined in a proximal end thereof for receiving a driving tool (e.g., screw driver) (not shown) configured to screw the threadedshaft64 of thescrew member60 into a hole in bone as the driving tool rotates thehead62 of thescrew member60. In particular, thescrew member60, while assembled to thescrew housing20, is configured to be screwed to a vertebral body such as the lateral mass of the “atlas” vertebra (the “atlas” vertebra is anatomical parlance for the commonly designated C1 vertebra—not shown).

With continued reference toFIGS. 1 and 4, theanvil30 of thepolyaxial bone screw10 is threaded into thescrew housing20 and positioned on thehead62 of thescrew member60 and in locking engagement with thespring40. Theanvil30 includes anannular anvil body32, which may be cylindrically-shaped, and defines asaddle34 configured to support the spinal rod “R” (FIG. 6). Thesaddle34 may be U-shaped. Theannular anvil body32 includes a threadedouter surface32athat is threadably engaged with the threadedinternal surface20eof thescrew housing20 and positioned atop thehead62 of thescrew member60. The threadedouter surface32afurther includes a pair ofside slots32bextending axially along the threadedouter surface32 on opposed sides of the threadedouter surface32a. One of theslots32breceives thespring40 to enable thespring40 to rotatably lock theanvil30 in position relative to thescrew housing20 such that the rod-receivingchannel22 of thescrew housing20 and thesaddle34 of theanvil30 are aligned. Theannular anvil body32 defines a central opening36 therethrough to provide screw-driving access to the drive recess62bof thescrew member60.

As seen inFIGS. 6-8, thescrew housing20 is configured to be polyaxially movable (e.g., pivotable and rotatable) relative to thescrew member60, for example, to accommodate the spinal rod “R” at various angular and/or rotational orientations. For instance, thescrew housing20 is movable in a first direction relative to thescrew member60 to receive theneck63 of thescrew member60 within thenotch28. With theneck63 positioned within thenotch28, thescrew member60 is pivoted away from the longitudinal axis “L” of thescrew housing20 to define a first pivot angle “α” relative to the longitudinal axis “L”. Although the first pivot angle “α” is shown to measure about 60 degrees, in certain embodiments, the first pivot angle “α” may range between 50 degrees to about 70 degrees, or more preferably between about 55 degrees to about 65 degrees. In some embodiments, the first pivot angle “α” may range between 45 degrees to about 90 degrees.

Thescrew housing20 is also movable in conical directions “CD” (FIG. 2A) relative to thescrew member60 that do not position thescrew member60 in registration with thenotch28 when thescrew member60 is pivoted away from the longitudinal axis “L.” These conical directions “CD” include medial-lateral directions (e.g., directions transverse to the spinal rod “R”) and (e.g., cranial-caudally and in-plane with spinal rod “R”—FIG. 7), at a second pivot angle “β”. For instance, thescrew housing20 is movable in a second direction (e.g., conical directions) relative to thescrew member60 to engage theneck63 of thescrew member60 at thedistal end20bof thescrew housing20. With theneck63 engaged with thedistal end20b, thescrew member60 is pivoted away from the longitudinal axis “L” of thescrew housing20 to define a second pivot angle “β” relative to the longitudinal axis “L”. Although the second pivot angle “β” is shown to measure about 45 degrees, in certain embodiments, the second pivot angle “β” may range between about 40 degrees to about 50 degrees. In some embodiments, the second pivot angle “β” may range between about 35 degrees to about 55 degrees.

In this arrangement, thenotch28 is configured to provide about ⅓ more angulation between thescrew member60 and thescrew housing20 in the first pivot angle “α” as compared to the second pivot angle “β”. Such arrangement helps to optimize angulation while maintaining structural integrity/strength ofscrew housing20.

Manufacturing of thepolyaxial bone screw10 may involve machining thescrew housing20, theanvil30, thepin50, thescrew member60, and theset screw70 in a lathe or screw machine. Thenotch28 of thescrew housing20 may be notched out of thescrew housing20 in a separate milling operation. Thespring40 may be separately coiled.

In assembling thepolyaxial bone screw10, the threadedshaft64 of thescrew member60 is passed through thescrew housing20 until thehead62 of thescrew member60 is rests on theseat25aof thescrew housing20. Next, the threadedouter surface32aof theanvil30 is threaded along the threadedinternal surface20eof thescrew housing20 until it seats onto thehead62 of thescrew member60 with theU-shaped saddle34 of theanvil30 aligned with the rod-receivingchannel22 of thescrew housing20. Thepin50 and thespring40 are then inserted into thetransverse hole26 of thescrew housing20. A staking tool (not shown) may then utilized to deform the edges of thetransverse hole26 of thescrew housing20 to fixedly retain thepin50 and thespring40 in thetransverse hole26 such that thespring40 is disposed in frictional engagement with one of theside slots32bof theanvil30 and with thehead62 of thescrew member60.

In use, once thescrew member60 of thepolyaxial bone screw10 is screwed into bone (e.g., vertebral body) thescrew housing20 of thepolyaxial bone screw10 can be movable relative to thescrew member60 through any of the angles detailed above to enable thescrew housing20 to receive the spinal rod “R” in the rod-receivingchannel22 of thescrew housing20. The frictional engagement between thehead62 of thescrew member60 and thespring40 helps maintain thescrew member60 and thescrew housing20 at a desired angular orientation with respect to one another. Once the spinal rod “R” is supported in thescrew housing20 on theanvil30, the spinal rod “R” can be secured to thepolyaxial bone screw10 by threading theset screw70 into thescrew housing20 against the spinal rod “R,” as seen inFIG. 8. Before fully tightening theset screw70, thescrew housing20 and the spinal rod “R” therein can be further manipulated and/or pivoted relative to thescrew member60 to achieve a desired angular position of the spinal rod “R.” Once the desired angular position of the spinal rod “R” is achieved, theset screw70 can be fully tightened to fix the angular relationship between thescrew housing20 and thescrew member60 of thepolyaxial bone screw10.

The polyaxialbone screw system10, or components thereof, may be formed from any suitable biocompatible material, including, for example, metals (e.g., a stainless steel, cobalt, chrome, titanium, and titanium alloy), polymers (e.g., PEEK, polyphenylsulfone, polyetherimide, polycarbonate, polyethylene, polypropylene, polyacetal, or other such engineering resin), or combinations of the aforementioned materials.

Persons skilled in the art will understand that the structures and methods specifically described herein and shown in the accompanying figures are non-limiting exemplary embodiments, and that the description, disclosure, and figures should be construed merely as exemplary of particular embodiments. It is to be understood, therefore, that the present disclosure is not limited to the precise embodiments described, and that various other changes and modifications may be effected by one skilled in the art without departing from the scope or spirit of the disclosure. Additionally, the elements and features shown or described in connection with certain embodiments may be combined with the elements and features of certain other embodiments without departing from the scope of the present disclosure, and that such modifications and variations are also included within the scope of the present disclosure. Accordingly, the subject matter of the present disclosure is not limited by what has been particularly shown and described.

Claims (18)

The invention claimed is:

1. A polyaxial bone screw device, comprising:

a screw having a head and a shaft;

a screw housing defining a bore that extends along a longitudinal axis, the screw housing including:

a basewall defining an aperture to receive a portion of the screw;

opposed sidewalls that extend from the basewall and define a rod-receiving channel; and

a transverse hole extending at least partially through one of the opposed sidewalls and being in communication with the bore;

an anvil disposed within the screw housing, the anvil having a body including a threaded surface for threadably mating the anvil within the screw housing and preventing the anvil from moving in a proximal direction upon application of a proximal force, the body of the anvil defining a saddle shaped surface for receiving a spinal rod seated within the rod-receiving channel; and

a spring disposed in the transverse hole of the screw housing, extending into the bore of the screw housing and applying a friction force to the screw head when the screw head is seated against the basewall of the screw housing.

2. The polyaxial bone screw device ofclaim 1, wherein the basewall further defines a notch configured to receive a portion of the screw.

3. The polyaxial bone screw device ofclaim 2, wherein when the screw is positioned along the longitudinal axis, the screw is pivotable in a first direction relative to the screw housing at a first angle and receivable within the notch, and pivotable in a second direction relative to the screw housing at a second angle different than the first angle.

4. The polyaxial bone screw device ofclaim 3, wherein the first angle is between approximately 50 degrees and 70 degrees relative to the longitudinal axis of the screw housing and the second angle is between approximately 35 degrees and 55 degrees relative to the longitudinal axis of the screw housing.

5. The polyaxial bone screw device ofclaim 4, wherein the first angle is about 60 degrees and the second angle is about 45 degrees.

6. The polyaxial bone screw device ofclaim 1, wherein the spring directly engages the screw head and is configured to maintain the shaft at an angular position relative to the longitudinal axis of the screw housing.

7. The polyaxial bone screw device ofclaim 1, wherein the screw head includes a textured outer surface that is configured to facilitate frictional engagement with the spring.

8. The polyaxial bone screw device ofclaim 7, wherein the textured outer surface comprises an annular rib or a ridge.

9. The polyaxial bone screw device ofclaim 1, wherein the anvil is seated on the screw head and the spring directly engages the anvil.

10. The polyaxial bone screw device ofclaim 1, wherein the spring directly engages both the anvil and the head of the screw and maintains the shaft of the screw at an angular position relative to the longitudinal axis of the screw housing.

11. The polyaxial bone screw device of1, wherein the threaded surface defines a first axial slot.

12. The polyaxial bone screw device ofclaim 11, wherein the threaded surface further defines a second axial slot circumferentially spaced about the body of the anvil from the first axial slot.

13. The polyaxial bone screw device ofclaim 11, wherein the spring extends into the first axial slot.

14. The polyaxial bone screw device ofclaim 1, further comprising a pin disposed within the transverse hole and extending at least partially through the spring.

15. The polyaxial bone screw device ofclaim 1, further comprising a set screw threadably received within the bore of the screw housing to secure a spinal rod within the screw housing.

16. A method of assembling a polyaxial bone screw assembly, comprising:

providing a screw housing including a basewall and opposed sidewalls that extend from the basewall and collectively define a bore and a rod-receiving channel, the basewall defining a notch configured to receive a portion of a screw therein, the screw housing further defining a transverse hole extending through one of the opposed sidewalls and being in communication with the bore;

inserting a spring through the transverse hole of the screw housing, from an exterior of the sidewall into the bore of the screw housing, such that the spring is arranged to provide a friction force to a screw head when the screw is inserted into the bore of the screw housing.

17. The method ofclaim 16, further comprising:

inserting a pin into the transverse hole of the screw housing to support the spring.

18. The method ofclaim 16, further comprising:

inserting the screw into the bore of the screw housing;

inserting an anvil into the bore of the screw housing and into engagement with the head of the screw, the anvil having a body defining a slot;

positioning a portion of the spring into the axial slot; and

positioning a portion of the spring into direct engagement with the head of the screw.

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